Load bearing surface

ABSTRACT

An elastomeric load bearing surface with different load support characteristics in different directions. In one embodiment, the surface includes an elastomeric membrane that is oriented in only a single direction, for example, by compression or stretching. In another embodiment, the surface includes mechanical structures, such as connectors and variations in thickness that vary the load support characteristics in different directions. In another embodiment, a surface is both oriented and includes mechanical structures.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of U.S. patent applicationNo. 11/112,345, filed Apr. 22, 2005, now U.S. Pat. No. ______, whichclaims the benefit of U.S. Provisional Patent Application No.60/580,648, filed Apr. 22, 2005.

The present invention relates to load bearing surfaces, and moreparticularly to elastomeric load bearing surfaces, such as the seat orback of a chair or bench, or the support surface of a bed, cot or othersimilar product.

There are continuing efforts to develop new and improved load bearingsurfaces. In the context of general load bearing surfaces, the primaryobjectives of these efforts are to obtain a durable and inexpensive loadbearing surface. In the context of seating and other body-supportapplications, it is also important to address comfort issues. Forexample, with seating, it can be important to provide a surface that iscomfortable and does not create body fatigue over periods of extendeduse. Given that the load characteristics (e.g. stiffness, resiliency,force/deflection profile) desired in a particular surface will vary fromapplication to application, it is also desirable to have a load bearingsurface that is easily tunable to different applications during designand manufacture.

It is known to provide molded load bearing surfaces for a wide varietyof applications. For example, molded plastic chairs (e.g. lawn chairs)are available from a variety of well known suppliers. Although thesemolded chairs provide an inexpensive seating option, they do not providethe level of support and comfort available in more expensive loadbearing surfaces, such as conventional cushion sets. Rather, theyprovide an essentially linear force/deflection profile, which gives thetypical molded seating surfaces the feel of a drum or a trampoline. Inseating and other body-support applications, this may result in anuncomfortable and sometimes ergonomically unacceptable load bearingsurface. Further, the ability to tune the characteristics of aconventional molded seat is relatively limited. Different materials anddifferent material thicknesses can be used to provide a limited degreeof control over the characteristics of the seat, but this level ofcontrol is not sufficient in many applications.

There is also an increasing use of elastomeric fabrics in the seatingindustry. Elastomeric fabrics can provide a comfortable, ventilatedseating structure. Elastomeric fabrics are typically manufactured from acomplex weave of high tech elastomeric monofilaments and multifilamentyarns. The process results in a relatively expensive surface. Althoughelastomeric fabric surfaces can be quite comfortable in manyapplications, they typically deflect like a sling when a load isapplied. Some ergonomic specialists refer to this type of deflection as“hammocking” and consider it undesirable because it can cause the hipsto rotate upward. To minimize hammocking, many suspension seats arestretched quite tightly to reduce the amount of deflection that occursunder load. This can reduce the cushion-like feel of the seat making itfeel more like a tightly stretched drum. As a result, elastomericfabrics may not be ideal in all applications.

Accordingly, there remains a need for an elastomeric load bearingsurface that is capable of providing non-linear force/deflection profilein response to different loads.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an elastomeric loadbearing surface having different support characteristics in differentdirections. In one embodiment, the support characteristics are varied(or decoupled) in directions that are perpendicular to one another.

In one embodiment of this aspect, the load bearing surface includes amolded elastomeric membrane that is decoupled by affecting theorientation of the structure of the membrane on a molecular level. Inthis embodiment, the molded elastomeric membrane may be oriented bycompressing or stretching the membrane in one direction to the extentnecessary to increase the alignment of the crystalline structure of theelastomer. The orientation process varies the support characteristics ofthe membrane resulting in a membrane with significant elasticity in thedirection of orientation and a low level of creep. The orientationprocess leaves the membrane with minimal elasticity in the directionperpendicular to the oriented direction. The reduced creep enables theuse of thinner, and therefore less stiff, molded materials as a loadbearing surface, thus reducing material costs and increasing comfort.

In another embodiment, the molded elastomeric membrane includesmechanical structure that affects the support and load bearingcharacteristics of the membrane. In this embodiment, the membrane mayinclude without limitation slits, channels, undulations or otherintegral elements that provide “slack” in one direction. If desired, themembrane may be oriented and include mechanical decoupling structure.

In yet another embodiment, the membrane is segregated into a pluralityof nodes that provide a degree in independence from one location on themembrane to another. In one embodiment, the membrane defines a pluralityof interconnected geometric shapes. For example, the membrane mayinclude a plurality of square or triangular nodes that areinterconnected by integral connector segments. The characteristics ofthe connector segments may be varied to control the supportcharacteristics of the membrane. For example, the membrane may includenon-planar connector segments that can flex or otherwise deform underload to provide the membrane with “slack.”

In a second aspect, the present invention provides a multi-layer loadbearing surface. In an embodiment of this aspect of the presentinvention, the load bearing surface includes interacting upper and lowerlayers. The upper layer may include a plurality of loosely connectednodes. In one embodiment, the upper layer is a molded sheet having aplurality of nodes interconnected by integral connector segments. Theupper layer may include an integral protrusion extending from each nodetoward the lower layer. The protrusions may be interfitted withcorresponding structure in the lower layer. The multi-layer load bearingsurface may also include springs elements disposed between the upper andlower layers. The spring elements may be integral with the upper layeror the lower layer. For example, the lower layer may include a pluralityof integrally molded flexible arms adapted to receive the protrusions ofthe upper layer. In one embodiment, the lower layer may be a decoupledmolded elastomeric membrane.

The present invention also provides a method of manufacturing a loadbearing surface from an elastomeric material. The method generallyincludes the steps of (a) molding an elastomeric membrane and (b)orienting the elastomeric membrane in one direction by stretching theelastomeric membrane in that direction or by compressing the elastomericmembrane in such a way as to cause it to flow in that direction. Theelastomeric membrane is stretch or compressed to a point where there isan increase in the alignment of the crystalline structure of theelastomeric material in the oriented direction. In one embodiment, themethod further includes the step of molding the elastomeric membranewith a structure that mechanically decouples the membrane in a directiondifferent from that in which the membrane is oriented. This decoupleddirection may be perpendicular to the oriented direction.

In one embodiment, the membrane is compressed by the steps of (a)constraining the membrane on all sides except those sides correspondingwith the desired direction of orientation and (b) applying a compressionforce to the membrane such that the material of the membrane flows inthe unconstrained direction to increase the alignment of the crystallinestructure of the membrane in the direction of flow.

The present invention further provides a method of manufacturing amulti-layer load bearing surface. The method generally includes thesteps of (a) producing an upper surface having a plurality of nodesinterconnected by connector segments, (b) producing a lower layeradapted to interface with the upper layer at the nodes and (c) combiningthe upper layer and the lower layer with spring elements disposed at theinterface locations. In one embodiment, the upper layer includes anintegral axel extending from each node and the lower layer includesintegral spring arms that receive the axels.

The present invention provides a strong, yet flexible load bearingsurface. The elastomeric load bearing surfaces are relativelyinexpensive to manufacture, and provide a light weight surface that canbe ventilated to inhibit heat retention. The decoupled elastomericmaterial exhibits support characteristics that are particularly wellsuited for use in seating applications because it provides differentdegrees of elasticity and support in different directions. For example,the decoupled elastomeric material can provide a seating structure withelasticity in the left to right direction, but not in the front to backdirection. Further, by increasing the alignment of the crystallinestructure of the elastomeric material, the level of creep in themembrane can be dramatically reduced. In the two layer embodiments, thesecond layer provides additional control over up/down (or z-axis)displacement of the load bearing surface. This permits more control overthe support and comfort characteristics of the seat.

These and other objects, advantages, and features of the invention willbe readily understood and appreciated by reference to the detaileddescription of the preferred embodiment and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a load bearing surface in accordancewith one embodiment of the present invention.

FIG. 2A a perspective view of an alternative load bearing surface havinga plurality of nodes.

FIG. 2B is an enlarged perspective view of a portion of the load bearingsurface of FIG. 2A.

FIG. 3A is a top plan view a molded elastomeric membrane prior toorientation.

FIG. 3B is a top plan view the molded elastomeric membrane duringorientation.

FIG. 3C is a top plan view the molded elastomeric membrane afterorientation.

FIG. 4 is a sectional view of the molded elastomeric membrane takenalong line IV-IV of FIG. 3C.

FIG. 5A is a perspective view of a first alternative load bearingsurface.

FIG. 5B is a sectional view of the first alternative load bearingsurface taken along line VB-VB.

FIG. 6A is a perspective view of a second alternative load bearingsurface.

FIG. 6B is a sectional view of the second alternative load bearingsurface taken along line VIB-VIB.

FIG. 7A is a perspective view of a third alternative load bearingsurface.

FIG. 7B is a sectional view of the third alternative load bearingsurface taken along line VIIB-VIIB.

FIG. 8A is an enlarged cross-sectional view of a portion of anelastomeric membrane having an integral edge.

FIG. 8B is a cross-sectional enlarged view of a portion of anelastomeric membrane having a first alternative integral edge.

FIG. 8C is an enlarged cross-sectional view of a portion of anelastomeric membrane having a second alternative integral edge.

FIG. 9 is a perspective view of a two layer load bearing surface inaccordance with one embodiment of the present invention.

FIG. 10 is an enlarged perspective view of a portion of the load bearingsurface of FIG. 9.

FIG. 11 is an exploded of the load bearing surface showing a singlespring and single node and a portion of the lower layer.

FIG. 12 is a top plan view of an alternative lower layer.

FIG. 13 is a top plan view of a second alternative lower layer.

FIG. 14 is a perspective view of an alternative lower layer with anintegral spring element.

FIG. 15 is a perspective view of a second alternative lower layer withan integral spring element.

FIG. 16 is a perspective view of an alternative top layer withtriangular nodes.

FIG. 17 is a perspective view of a single node of the alternative toplayer of FIG. 16.

FIG. 18 is an exploded perspective view of a load bearing surface havinga plurality of nodes, and a support frame.

FIG. 19 is a perspective view of the load bearing surface of FIG. 18attached to the support frame.

FIG. 20 is a close-up view of a snap for attaching the load bearingsurface of FIG. 18 to a support frame.

FIG. 21 is a plot of various stress-strain curves.

DETAILED DESCRIPTION OF THE CURRENT EMBODIMENTS

A load bearing surface 10 according to one embodiment of the presentinvention is shown in FIG. 1. The load bearing surface 10 shown in FIG.1 is a molded membrane that may be suspended from a support structure,such as a chair seat frame 100 (shown in FIGS. 18 and 19). The loadbearing surface 10 includes support characteristics that differ indifferent directions. For example, the load bearing surface may providesignificant elastic support in the x direction while providingrelatively little support in the y direction. This “decoupling” of thesupport characteristics of the load bearing surface provides a highdegree of comfort. By way of disclosure, the present invention isdescribed in connection with various alternative embodiments intendedprimarily for use in seating applications. The present invention is not,however, limited to use in seating applications, but may also beincorporated into other load bearing applications. The supportcharacteristics of the molded membrane are highly adjustable, therebypermitting the load bearing surface 10 to be tailored to support avariety of loads in a variety of different applications.

In the embodiment of FIG. 1, the load bearing surface 10 includes amolded elastomeric membrane 12. In the illustrated embodiment, themembrane 12 is molded from a thermoplastic polyether ester elastomericblock copolymer. Suitable materials of this type include that availablefrom DuPont under the Hytrel® trademark, and that available from DSMunder the Arnitel® trademark. A variety of alternative elastomers may besuitable for use in the present invention. The thickness of the moldedmembrane 12 will vary from application to application dependingprimarily on the anticipated load and the desired stiffness of thesurface, but the support portion of the membrane may have an averagethickness prior to any desired orienting of approximately 20-40 mils instandard seating applications.

In one embodiment, the molded membrane 12 is oriented in one direction(i.e. the x direction) to provide creep resistance and elasticity in thedirection of orientation. The membrane 12 is oriented by increasing thealignment of the crystalline structure of the elastomeric membrane on amolecular level so that its support and other load bearingcharacteristics are altered. More particularly, a molded, un-orientedelastomeric membrane is typically comprised of a plurality ofspherulites, which are created during the growth of the polymer by theformation of crystalline lamellae in helical strands radiating from anucleation point. In an oriented membrane, at least some of thespherulites are destroyed and the crystalline lamellae are aligned inone direction. Typically, the membrane will be oriented to such a degreethat the oriented membrane 12 has materially different load bearingcharacteristics in the oriented direction than in other directions.

One method for orienting the membrane 12 is through stretching. Theamount of stretch required to obtain the desired alignment will varyfrom application to application, but in most applications the desireddegree of alignment will occur when the membrane is stretched to roughlytwo times it original dimension. In one embodiment, the membrane isstretched beyond its elastic limit to a distance between approximately 3to 8 times it original dimension, using approximately 1830 lbs. offorce. Because the membrane is stretched beyond its elastic limit, itrecovers to an intermediate dimension that is deformed from its originallength. This deformation is non-recoverable, permanent deformation. As aresult of this orientation and non-recoverable deformation, a degree ofpermanent deformation is removed from the oriented membrane such thatwhen subsequent stresses on the oriented membrane within the desirednormal operating load are applied (for example in the range ofapproximately 100-300 lbs. for a seating application), the membraneresists permanent deformation over time (i.e. creep).

Although the membrane may be oriented by stretching using a variety ofmethods and under a variety of conditions, a number of parameters may becontrolled to provide the membrane with a desired amount of orientation.For instance, in one embodiment, the molded membrane is stretched with ashort time, such as 10-15 minutes, after it is removed from the mold, sothat the membrane is still warm when it is stretched. This reduces theforce that is necessary to stretch and therefore orient the membrane. Inanother embodiment, the membrane is stretched at a rate of about 1 inchper second, until it has reached the desired deformation. A slow,controlled stretch aids in maintaining a uniform orientation across themembrane. In another embodiment, a cyclic orientation may be performed,wherein the membrane is oriented by stretching it to a first distance,then relaxed to a second, intermediate distance, and then stretched to asecond distance greater than the first. The sequence may be repeated asmany times as necessary to achieve the desired orientation. In onespecific embodiment, the membrane is stretched to 2 times its originallength, relaxed to 1.5 times the original length, then stretched to 3times the original length. A cyclic orientation process helps compensatefor any irregularities within the membrane material to provide a uniformstretch, because areas of greater or lesser stretch will even out aftermultiple cycles.

In addition to reducing creep, the stretching of a molded membrane maybe utilized to control the stiffness of the load bearing surface, and,ultimately, the comfort level of the surface. First, as noted above,orienting a membrane in one direction provides an increase in elasticityin the material in that direction. The increased elasticity decreasesthe stiffness of the material in the oriented direction, and thereforeaffects the comfort of the material in locations of orientation. Second,as noted above, in use, the molded membrane may be suspended from achair seat frame. Typically, the membrane is supported in tension on theframe with a desired amount of pre-load. Variations in the pre-loadchange the stiffness of the membrane, and therefore affect the comfortlevel of the load bearing surface. In one embodiment, where the size ofthe frame and the original membrane size are held constant, thestiffness characteristics of the material can be altered by changing theamount of permanent deformation given to the membrane before it isattached to the frame. A great amount of stretch during orientationprovides a looser, less stiff load bearing surface when the membrane ismounted to the support frame.

Although the elastomeric membrane 12 may be oriented by stretching themembrane, it may be possible in some application to orient the membrane12 using other processes. For example, it may be possible to orientcertain materials by hammering or other forms of compression, ratherthan stretching the membrane 12. It should be noted that manyelastomeric materials, including molded Hytrel®, have essentially noelasticity and are susceptible to a high degree of creep when in amolded form. As noted above, the orientation process of the presentinvention causes a significant change in the properties of theelastomeric material. For example, orientation of the membrane 12increases the elasticity of the material and decreases its inherentsusceptibility to creep. The elastomeric membrane 12 of FIG. 1 alsoincludes a plurality of undulations 14 that provide “slack” in thedirection perpendicular to the direction of orientation (i.e. the ydirection). When a load is applied to the membrane 12, the undulations14 can undergo a “flattening” that permits the membrane 12 to expand inthe y direction. The undulations 14 and other mechanical decouplingstructures are described in more detail below.

The membrane 12 of FIG. 1 also includes an integral edge 16 that may bemounted directly to the desired support structure (not shown), such asthe seat frame of a chair. In the illustrated embodiment, the edge 16extends around the periphery of the membrane 12 and is significantlythicker than the remainder of the membrane 12. The edge 16 may includeintegral snap or other attachment features (not shown) that facilitateattachment of the membrane 12 to the support structure. Alternatively,the edge 16 may be attached using fasteners (not shown), such as screwsor bolts. The edge 16 does not necessarily extend entirely around themembrane 12, but may instead include one or more segments located atdifferent locations around the periphery. Alternatively, an edge segmentmay be located in each corner of a rectangular membrane (not shown). Theedge 16 is also not necessarily located on the periphery of the membrane12. In some applications, it may be desirable to have one or more edgesegments located within the interior of the membrane 12. For example, inan elongated surface, an edge segment may be included in the centralinterior of the membrane to provide a central mounting location (notshown). Three alternative edge constructions are shown in FIGS. 8A-C.FIG. 8A shows an edge 16′ having holes 17′ to facilitate attachment ofthe edge 16′ to a support structure (not shown). For example, fasteners(not shown) may pass through the holes 17′. Alternatively, the holes 17′may be fitted over attachment structure on the support structure (notshown), such as post. FIG. 8B shows an edge 16″ that is substantiallycircular in cross section. FIG. 8C shows an edge 16′″ that issubstantially square in cross section.

A variation on the embodiment shown in FIG. 8A is shown in FIGS. 18-20.In this embodiment, the edge 160 of the membrane 320 includes a seriesof receptacle holes 170. As shown, the receptacle holes 170 are evenlyspaced in rows along the integral peripheral edge 160. The receptacleholes 170 are shaped and spaced to align with corresponding snaps 104extending from the seat frame 100. In this embodiment, the membrane iseasily attached to the frame 100 by inserting each of the snaps 104 intoa corresponding receptacle hole 102. As shown in FIG. 20, the snaps 104include an outer edge 106 that may be tapered. The tapered shape helpsto locate the membrane on the frame, and to pull any slack out of themembrane in the x and y directions as the membrane is attached to theframe. The side edges 108 and 114 may be tapered more than the remainingedges in order to pull the membrane tight in the y direction. In oneembodiment, the edge 160 is not oriented and is at least three times asthick as the oriented section in order to prevent creep in the integraledge. The integral edge 160 may be used for multiple purposes in themanufacturing process. For instance, the edge 160 (or 16 shown in theprevious embodiments) may be used as a grip surface for a set of clamps(not shown) used to orient the membrane by stretching. The addedthickness of the edge 160 makes this possible, because it provides arigid surface for contacting the clamps that will not stretch with therest of the membrane. After the membrane is oriented, the same edge maythen be used to mount the membrane to the support frame using one of themultiple techniques noted above.

As noted above, the elastomeric membrane 12 is molded using conventionaltechniques and apparatus. For example, the elastomeric membrane 12 maybe injection molded using a conventional injection molding apparatus(not shown) having a die that is configured to provide a membrane withthe desired shape and features. In this embodiment, the elastomericmembrane 12 is manufactured by injecting the desired material into thedie cavity. The die is designed to provide a molded blank (See FIG. 3A)that will take on the desired shape once any desired orientation havetaken place. For example, the dies are configured to form a part thatwill have the desired shape and dimensions after the orientation step iscomplete. After molded, the molded membrane may be stretched orotherwise oriented in one direction (See FIG. 3B). If orientation isachieved through stretching, the precise amount of stretch to be appliedto a given membrane will depend on the configuration of the membrane andthe desired support characteristics. In many applications, it will benecessary to stretch the membrane to at least twice, and preferablythree times, its original length to achieve the desired alignment. Themembrane may be stretched using conventional techniques and apparatus.In one embodiment, a set of clamps (not shown) may be configured toclamp onto the integral edge of the membrane during stretching. As aresult of the plastic deformation, and the increase in alignment of thecrystalline structure, the membrane 12 will not fully return to itsoriginal length after being released from the stretching equipment.Rather, the oriented membrane 12 will be elongated a certain portion ofthe stretched distance, with the precise amount of elongation beingdependent in large part on the material characteristics of the membranematerial (See FIG. 3C). Once any desired orientation has taken place,the membrane 12 can be mounted directly to the support structure usingessentially any mounting technique.

An plot showing an example of the changes in material properties of aparticular molded membrane is shown in FIG. 21, which includes threedifferent stress-strain curves. The curves show engineeringstress-strain (i.e. no accommodation for changes in surface area duringdeformation). Line A shows the stretching of an original, un-oriented,membrane to failure at 0.05 inches of stretch per second. The failureoccurred at approximately 2250 lbs., at which point the material wasstretched to about 825% of its original length. Line B shows theorientation of the same type of material by stretching the material toabout 650% of its original length. This orientation includes one cycle,where the material was relaxed after stretching the membrane to 100% ofits original length, before continuing the orientation process. In thiscase, the material recovers to a final length that is over 3.5 times itsoriginal length. This shows the plastic deformation of the materialafter orientation. Line C shows the stretching to failure of theoriented material. The material fails at approximately 2400 lbs. offorce. As can be seen by comparing the elastic regions of lines A and Crespectively, the oriented membrane shown in line C has a lower modulusof elasticity, such that it is more elastic than the original materialand capable of completely recovering to its oriented length afterreceiving normal operating loads (for example, about 180 lbs.).

In one embodiment, a membrane that has been oriented by stretching canbe attached to a support frame manually—without the use of stretchingequipment—before the stretched material has completely recovered to itsfinal size. This attachment must take place within a relatively shorttime after the membrane has been stretched, so that little or no load isrequired to attach the membrane, for example, by inserting the snaps 104into the receptacle holes 102. The membrane then continues to recoverafter is it attached to the frame, such that after it reaches its finalsize the membrane is stretched in tension on the frame. In oneembodiment, the final recovered size of a membrane after orientation maybe pre-determined, such as by experimentation or calculation, such thatthe membrane can be placed on the frame with zero of no load, and thenrecover to a final size with a desired amount of pre-load. In oneembodiment, the desired amount of pre-load is between 75 and 250 lbs. Ifthe membrane is attached before full recover, it is desirable to allowit to recover for a period of time prior to its final use.

As an alternative to stretching, the membrane 12 may be oriented bycompression. In one embodiment for orienting by compression, themembrane 12 is placed in a die or other structure (not shown) thatconstrains the membrane 12 on all sides other than at least one sidethat corresponds with the desired direction of orientation. Opposedsides may be unconstrained to permit the material of the membrane 12 toflow from both sides along the direction of orientation. Alternatively,only a single side may be unconstrained, thereby limiting material flowto a single side. A compressive force is then applied to the membrane12. For example, a press can be used to compress the membrane 12 withinthe die. Sufficient compressive force is applied so that the materialbegins to flow in the unconstrained direction. This in effect causes themembrane 12 to extend and its crystalline structure to becomeincreasingly aligned in the direction of orientation. The amount offorce applied to the membrane 12 may vary from application depending onthe desired degree of alignment or orientation. Although described inconnection with orientation of the entire elastomeric membrane 12, insome application it is not necessary to orient the entire membrane 12.Rather, in some applications, it may be desirable to orient only selectportions of the membrane. For example, in some applications it may bedesirable to orient only select peripheral portions of the membrane.When desirable, this may be achieved by applying localized stretching orlocalized compression of the membrane. In other applications, selectedportions of the membrane may have a reduced thickness, such thatprimarily these selected portions will stretch and become orientedduring the orientation process.

The use of a molded membrane in the present invention provides theability to easily create textures on the membrane, provide the membranewith essentially any desired contour and vary the thickness of themembrane in different locations. Although not shown, the upper surfaceof the membrane may be smooth or may be textured to provide theappearance of leather, fabric or other desired textures. Similarly, theupper surface of the membrane may be provided with essentially anyconceivable design elements (not shown), such as tiny bumps,corrugations, perforations or a spider web pattern. The use of contoursand varying thicknesses across the membrane 12 permits localized controlover the support characteristics of the membrane 12. For example, themembrane 12 may be thicker in regions where increased support isdesired.

Various alternative embodiments of the present invention will bedescribed in the following paragraphs. In each of these alternativeembodiments, the elastomeric membrane may be oriented in one directionto reduce creep and provide the membrane with a desired level ofelasticity in the direction of orientation. It is not, however,necessary to orient the membrane in all applications. Rather, inapplications where the elasticity and creep resistance provided byorientation are not necessary (or not desirable), variation in thesupport characteristics of the membrane in different directions may beachieved solely by variations in the structure of the membrane.

An alternative embodiment is shown in FIG. 5A-B. In this embodiment, themembrane 12′ defines a plurality of slits or apertures that decouple thestiffness of the membrane in the x and y directions. More specifically,the membrane 12′ defines a plurality of apertures 26′ that permit aspecific amount of extension of the membrane in the desired direction(i.e. the y direction) without significant stretching of the membrane12′. The apertures 26′ may be elongated as shown in FIG. 5A. As shown,the apertures 26′ may be staggered across the surface of the membrane12′ with the precise shape, number, location and size of the apertures26′ being dictated primarily by the desired support characteristics. Asshown in FIG. 5B, the membrane 12′ may be molded with a bead 27′ aroundeach aperture 26′ to reduce the possibility of tearing. As noted above,the membrane 12′ may be oriented in the x direction as described abovein connection with membrane 12.

A second alternative embodiment is shown in FIGS. 6A-B. In thisembodiment, the membrane 12″ includes undulating variations 26″ thatdecouple the stiffness of the membrane 12″ by providing “slack” in onedirection (e.g. the y direction). As shown in FIG. 6B, the undulatingvariations 26″ may be sinusoidal when viewed in cross-section.Alternatively, the undulating variations 26″ may resemble an accordionor pleated configuration when view in cross-section. The undulations mayfollow essentially any contour that varies in the z direction. In thisembodiment, the undulations 26″ are arranged parallel to one another. Asa result, the undulations 26″ cooperate to provide slack in essentiallyone direction. The undulations 26″ may, however, be in a non-parallelarrangement when appropriate to provide the desired supportcharacteristics. The number, size, shape and location of the undulations26″ can be tuned to provide control over the support characteristics ofthe membrane 12″.

A third alternative embodiment is shown in FIG. 7A-B. In thisembodiment, the membrane 10′″ includes a plurality of ribs 26′″extending at least partially across the membrane 12′″. In oneembodiment, the membrane 12′″ includes a plurality of parallel ribs26′″. The ribs 26′″ provide the membrane 12′″ with additional materialthat reduces the force required to stretch the membrane 12′″ in thedirection perpendicular to the ribs 26′″ (i.e. the y direction), whileat the same time having little effect on the force required to stretchthe membrane 12′″ in the direction parallel to the ribs (i.e. the xdirection). The number, size, shape and location of the ribs 26′″ can betuned to provide control over the support characteristics of themembrane 12′″.

The load bearing surface may optionally be divided into a plurality ofnodes. The molded elastomeric membrane 112 shown in FIGS. 2A-B includesa plurality nodes 118 interconnected by a plurality of connectorsegments 120, 122. As perhaps best shown in FIG. 2B, the nodes 118 andconnector segments 120, 122 are integrally formed as a single moldedpart. In the embodiment of FIGS. 2A-B, the membrane 112 includes aplurality of substantially square, equal-sized, regularly-spaced nodes118. The nodes 118 need not, however, be of equal-size or beregularly-spaced. Rather, the nodes 118 may vary in size, shape, spacingor other characteristics in different regions of the membrane 112 toprovide localized control over the support characteristics of themembrane 112 in the different regions. Although the nodes 118 of thisembodiment are substantially square, they may vary in shape fromapplication to application. For example, circular, triangular,rectangular or irregular shaped nodes may be desired in certainapplications. The illustrated nodes 118 have a generally planar uppersurface 124, but the upper surface 124 may be contoured. For example,the nodes 118 may have a convex upper surface (not shown). It shouldalso be recognized that the spaces 126 defined between the nodes 118 andthe connector segments 120, 122 provide a ventilated membrane 112. Thesize, shape and configuration of the spaces 126 can be tailored toprovide the desired balance between ventilation and supportcharacteristics.

As noted above, the nodes 118 are interconnected by a plurality ofconnector segments 120, 122 (See FIG. 2B). The support characteristicsof the membrane 112 are affected by the number, size, shape and othercharacteristics of the connector segments 120, 122. In this embodiment,the membrane 110 is configured to provide elastic support along onedirection. Accordingly, the connector segments 120 joining the nodes 118in the oriented direction x are substantially planar. As a result, theelastomeric membrane 112 undergoes a stretching action in the directionof orientation when a load is applied. In this embodiment, the membrane112 is configured to have minimal elastic response in the y direction(i.e. the direction perpendicular to the oriented direction).Accordingly, the connector segments 122 joining the nodes 118 in the ydirection are generally non-planar following a somewhat U-shaped arc. Asa result, the connector segments 122 provide the membrane with “slack”in the direction perpendicular to the oriented direction. Under load,the non-planar connectors 122 undergo a bending action that essentiallyflats the connectors taking the “slack” out of the membrane 112. Thispermits the membrane 112 to undergo a certain amount of expansion in thedirection of the slack without stretching of the membrane 112. Theamount of load required to achieve this expansion can be built into themembrane 112 by tuning the design and configuration of the connectorsegments 120, 122. Although the precise force required to achieve thebending action will vary, the bending action generally providessignificantly less resistance to the expansion of the membrane 112 andless elastic return than would normally result from a stretching action.As a result, the membrane 112 provides elastic support primarily in thedirection of orientation.

In addition, in an embodiment where a membrane is both oriented andincludes mechanical decoupling structure, the mechanical decouplingstructure, such as the nodes 118, can also be used to affect and controlthe locations of orientation of the membrane. For instance, in themembrane shown in FIGS. 2A and 2B, the connector segments 120 extendingin the direction of orientation have a reduced thickness than the nodes118 and the remainder of the membrane. As a result, when the membrane110 is oriented by stretching the membrane in the x-direction, thestretching and orientation occurs primarily within the connectingsegments 120. In the illustrated embodiment, these sections of reducedcross section extend in uniform rows in the y-direction, such that theycan stretch uniformly when pulled in the x-direction. The nodes 118remain substantially un-oriented. This allows substantial control overthe locations of orientation, and the stiffness of the load bearingsurface.

In another aspect, the present invention provides a multi-layer loadbearing surface 200. In the embodiment of FIGS. 9-11, the load bearingsurface 200 includes an upper layer 204 having a plurality of looselyconnected nodes 208, a lower layer 206 that interfaces with and supportsthe upper layer 204 and a plurality of spring elements 230 interposedbetween the upper layer 204 and the lower layer 206. In one embodiment,the upper layer 204 includes a plurality of interconnected nodes 208.The upper layer 204 may be a single molded sheet formed with integralconnector segments 212 that interconnect adjacent nodes 208. In theembodiment of FIGS. 9-11, the nodes 208 are square. But, the nodes 208may be of other shapes. For example, in the alternative embodiment ofFIGS. 16-17, the nodes 208′ are triangular. The characteristics of theconnector segments 212 are selected to provide the desired level ofinterdependence between adjacent nodes 208. For example, relativelyshort, thick connector segments 212 may be included when a high degreeof interdependence is desired between the nodes 208 and longer orthinner connector segments 212 may be included when a high degree ofindependence is desired. If desired, the connector segments 212 can becurved to the provide “slack” between the nodes 208, similar to theconnector segments 122 described above in connection with membrane 10.In the illustrated embodiment, the upper layer 204 further includes anaxel 216 (or other protrusion) extending from each node 208 toward thelower layer 206. As described in more detail below, the axels 216 areinterfitted with corresponding openings 218 in the lower layer 206. Theinterfitted relationship permits the lower layer 206 to shepherdmovement of the upper layer 204. The axels 216 may have various shapes.But, in the embodiment of FIGS. 9-11, each axel 216 includes anelongated cylindrical shaft. In the alternative embodiment, shown inFIGS. 16 and 17, each axel 216′ generally includes a shaft 200′terminating in a head 222′. The head 222′ is an inverted cone having atapered lower end 224′ that facilitates insertion of the axel 216′ intothe corresponding opening in the lower layer and a substantially flatupper end 226′ that resists removal of the axel 216′ from the opening inthe lower layer. The axel head 222′ permits the upper layer 204′ and thelower layer to be easily snap-fitted into an interlocking relationship.The head 222′ may alternatively include other interlocking shapes.

The lower layer 206 provides a support structure for the upper layer204. The lower layer 206 is optionally elastic and is optionallysegregated into nodes 240 corresponding with the upper layer nodes 208.In the embodiment of FIGS. 9-11, the lower layer 206 is a decoupled,molded elastic membrane similar to membrane 112 described above. Thelower layer 206 includes a plurality of square nodes 240 that areinterconnected by connector segments 242, 244. As with membrane 112, thelower layer 206 is oriented in the x direction and includes non-planarconnector segments 224 that provide slack in the y direction. Unlikemembrane 112, however, each node 240 defines an opening 218 adapted toreceive the axel 216 of the corresponding upper layer node 208.

The configuration of the nodes 240 and connector segments 242, 244 mayvary from application to application. A first alternative lower layer206′ is shown in FIG. 12. In this embodiment, the lower layer 206′ isoriented in the x direction. The lower layer 206′ includes square nodes240′ that are interconnected by connector segments 242′, 244′. Theconnector segments 242′ link the nodes 240′ in the x direction and areessentially planar to provide no slack in the oriented direction. Theconnector segments 244′ link the nodes 240′ in the y direction and arearcuate to provide slack in the y direction. A second alternative lowerlayer 206″ is shown in FIG. 13. This embodiment is essentially identicalto lower layer 206′, except that the nodes 240″ are generally circular.As with lower layer 206′, the connector segments 242″, 244″ of lowerlayer 206″ may provide slack in the y direction, if desired. Althoughthe lower layer is described in connection with various orientedconstructions, it is not necessary for the lower layer to be oriented orotherwise decoupled. Similarly, the lower layer 206 need not besegregated into distinct nodes.

As noted above, spring elements are interposed between the upper layer204 and the lower layer 206. Preferably (but not necessarily), a springelement 250 is disposed between each upper layer node 208 and thecorresponding lower layer node 240. As shown in FIGS. 9-11, springelements, such as a coil spring, may be fitted over each axel 216disposed between the upper layer 204 and lower layer 206. Thecharacteristics of the separate springs may vary from location tolocation to provide different support characteristics in differentportions of the load bearing surface.

The spring elements may alternatively be integrated into the lowerlayer. As show in FIG. 14, the lower layer 306 may include a pluralityof integral spring arms 350 that are integrally molded with the lowerlayer 306. The spring arms 350 are arranged so that a single spring arm350 is uniquely aligned with each of the upper layer nodes 208. Thespring arms 350 are cantilevered and are generally arcuate extendingfrom the lower layer 306 toward the upper layer 204. The upper end 352of each spring arm 350 is configured to engage the undersurface of thecorresponding upper layer node 208. Each spring arm 350 defines an axelopening 318 configured to receive the axel 216 of the correspondingupper layer node 208. In this embodiment, the axel opening 318 issmaller than the head of the axel so that the axel snap-fits into thespring arm 350. The arcuate spring arms 350 can be replaced by othercantilevered or otherwise resilient structures, such as arches or domes.

An alternative integral spring construction is shown in FIG. 15. In thisembodiment, the spring elements 450 each include an integral gimbal 460that facilitates movement of the axel 216 in essentially any direction,thereby giving the upper layer 204 more flexibility. The spring element450 includes a cantilevered arm 452 extending from the lower layer 406toward the upper layer 204. The spring arm 450 terminates in an integralgimbal 460. The gimbal 460 generally includes a pivot ring 462 and amounting ring 464. The pivot ring 462 is connected to the remainder ofthe spring arm 450 by a pair of flexible bridges 466. The bridges 466are diametrically opposed to one another on opposite sides of the pivotring 462. The pivot ring 462 is in turn connected to the mounting ring464 by a pair of flexible bridges 468. The mounting head bridges 468 arediametrically opposed to one another on opposite sides of the mountingring 464 and are offset approximately ninety degrees from the pivot ringbridges 466. In use, the pivot ring bridges 466 and mounting ringbridges 468 are sufficiently flexible to permit the mounting ring 464 topivot in essentially any direction as may be dictated by the loadtransferred by the axel 216. The characteristics of the gimbal 460 canbe turned to provide the desired support characteristics.

In yet another alternative embodiment, the spring elements may beincorporated into the upper layer rather than the lower layer. In thisembodiment, the spring element may be essentially identical to thespring elements described above.

The lower layer can be readily configured to provide localized controlover the support characteristics of the load bearing surface. Ifdesired, the characteristics of the spring elements may be varied indifferent regions of the lower layer to provide corresponding variationsin the support characteristics in the different regions. For example,the stiffness of select spring elements may be increased or decreased toprovide greater or lesser support, as desired. The shape, thickness,length or other characteristics of the spring elements may be varied toprovide the desired localized control.

The above description is that of various embodiments of the invention.Various alterations and changes can be made without departing from thespirit and broader aspects of the invention as defined in the appendedclaims, which are to be interpreted in accordance with the principles ofpatent law including the doctrine of equivalents. Any reference to claimelements in the singular, for example, using the articles “a”, “an,”“the” or “said,” is not to be construed as limiting the element to thesingular.

1. A load bearing surface comprising a molded elastomeric membrane, said membrane being oriented in a first direction, whereby said membrane provides different load bearing characteristics in said first direction than in a second direction.
 2. The surface of claim 1 wherein said membrane includes an integral edge, said integral edge adapted to permit mounting of said membrane to a support structure.
 3. The surface of claim 2 wherein said integral edge defines at least one receptacle hole, said receptacle hole adapted to receive a protrusion extending from said support structure.
 4. The surface of claim 3 wherein said integral edge extends along a first side of said membrane, and a second side of said membrane, said second side opposite said first side, said first and second sides extending perpendicular to said first direction.
 5. The surface of claim 4 wherein said membrane includes a first section having a first thickness and a second section having a second thickness, said first section extending substantially in said second direction.
 6. The surface of claim 5 wherein said integral edge has a third thickness, said third thickness being at least 3 times thicker than said first thickness.
 7. The surface of claim 3 wherein said mechanical structure includes a plurality of channels integrally formed with said membrane, said channels extending in substantially said first direction.
 8. The surface of claim 1 wherein said membrane defines a plurality of nodes interconnected by a plurality of connectors, said connectors extending in said first direction having different physical characteristics than said connectors extending in said second direction, whereby said membrane is decoupled at least in part by differences in said physical characteristics of said plurality of connectors.
 9. The surface of claim 1 wherein at least a portion of said membrane includes a crystalline structure having a greater degree of alignment in said first direction than in other directions.
 10. A method for manufacturing a load bearing surface, comprising the steps of: molding an elastomeric membrane; orienting at least a portion of the elastomeric membrane in only one direction until the crystalline structure of the membrane becomes sufficiently aligned in the one direction to provide the portion of the elastomeric membrane with load bearing characteristics in the one direction that are different from other directions.
 11. The method of claim 10 wherein said orienting step is further defined as stretching at least a portion of the elastomeric membrane in the one direction to at least approximately three times the original dimension of the portion of the membrane.
 12. The method of claim 11 wherein the molded membrane is stretched within a period of 15 minutes after it is removed from the mold, while the membrane is still in a heated condition.
 13. The method of claim 11 wherein the mold membrane is stretched to a sufficient distance that it is plastically deformed.
 14. The method of claim 11 wherein the membrane is stretched from an original distance to a first distance, then relaxed to a second distance between said original distance and said second distance, and then stretched to a third distance longer than said second distance.
 15. The method of claim 11 further including the steps of: molding the elastomeric membrane with an integral edge; and attaching the elastomeric membrane to a support structure by the edge.
 16. The method of claim 15 wherein the step of stretching the membrane includes pulling the membrane at the integral edge.
 17. The method of claim 15 wherein the step of attaching the membrane to a support structure includes inserting a plurality of protrusions on the support structure into a plurality of corresponding receptacles defined in the integral edge of the membrane.
 18. The method of claim 15 wherein the stretched membrane is attached to the support structure before it has recovered to a final length.
 19. The method of claim 10 wherein said orienting step is further defined as: constraining at least a portion of the elastomeric membrane on all sides except at least one unconstrained side corresponding with the one direction; compressing the portion of the elastomeric membrane until the material of the portion of the elastomeric membrane flows outwardly along at the unconstrained side in the one direction.
 20. A method for manufacturing a load bearing surface, comprising: molding an elastomeric membrane such that the membrane includes a plurality of nodes interconnected by a plurality of connectors, the connectors extending in a first direction, the connectors having a thickness that is less than the thickness of the nodes; orienting the elastomeric membrane by stretching the membrane in the first direction to a distance sufficient to plastically deform the membrane and to provide the crystalline structure of the membrane with a greater degree of alignment in the first direction; and mounting the membrane to a support structure before the membrane has recovered to a final length, the membrane continuing to recover after it is mounted to the support structure, the fully recovered membrane providing a desired about of tension between the support structure and the membrane.
 21. A load bearing surface comprising: a support structure; a molded elastomeric membrane, at least a portion of said membrane being oriented to have a crystalline structure with a greater alignment in a first direction than in a second direction, said membrane molded to include mechanical structure decoupling said membrane between said first direction and said second direction; and attachment means between said support structure and said membrane for supporting said membrane in tension on said support structure.
 22. The load bearing surface of claim 21 wherein said attachment means includes an integral edge molded into said membrane, said integral edge defining a plurality of receptacles, and a plurality of protrusions on said support structure, each of said protrusions being inserted into a corresponding one of said receptacles.
 23. The load bearing surface of claim 22 wherein said protrusions each include an outer edge, at least a portion of said outer edge being tapered.
 24. The load bearing surface of claim 23 wherein said outer edge includes first and second sidewalls facing in said second direction, and third and fourth sidewalls facing in said first direction, said first and second sidewalls having a greater degree of taper than said third and fourth sidewalls.
 25. The load bearing surface of claim 21, wherein portions of said membrane have a greater degree of orientation than other portions of said membrane, said portions of greater orientation having a greater degree of elasticity than said other portions.
 26. The load bearing surface of claim 25, wherein said membrane include a plurality of nodes interconnected by connector segments, said connector segments having a greater degree of orientation than said nodes.
 27. The load bearing surface of claim 26 wherein said nodes are arranged in a matrix. 